الوصف:
The U.S. Forest Service on the Willamette National Forest currently employs the “Disturbed Water Erosion Prediction Project” (WEPP) model to determine potential suspended sediment delivery from timber harvests or other treatment scenarios given user-defined hillslope parameters. At the time of this study there was no known calibration or testing of the model’s accuracy in steep, dissected terrain such as that of the Western Cascades of Oregon.
This analysis used the simplified web-based version of FSWEPP to predict suspended sediment output from three small catchments located on the H.J. Andrews (HJA) Research Forest. Basins were either clear-cut, 25% patch-cut, or in old-growth control conditions. Inputting long-term site data from on-the-ground measurements, WEPP model fields were populated with the most basin-representative information possible.
Four different model simulation strategies compared suspended sediment delivery both within individual basin scenarios, and also between the three basins.
Results indicated that WEPP tended to over-estimate suspended sediment outputs across the treated basin scenarios relative to long-term ground data. A crude Analysis of Variance (ANOVA) f-test compared the differences in total mean suspended sediments delivered or predicted within each basin. Subsequent numbers suggested that at least two of the basins’ means were significantly different between various model scenarios as well as the Andrews dataset.
Though Disturbed WEPP was ultimately not a convincing prediction tool in this investigation, the study provided both background and foundation for further model testing and calibration. Given the wealth of long-term data available from the HJA, the model may merit further ground-testing and calibration against the backdrop of this climate and terrain.